The present invention relates to a liquid infusion device used for continuously dispensing a predetermined amount of liquid drug little by little to blood vessel, extradural space, subctis, urinary bladder and the like, and more particularly to a liquid infusion device capable of minimizing liquid drug remaining in a bladder, whereby effectively utilizing liquid drug without waste.
Hitherto, as a device for dispensing a very small amount of liquid drug such as antibiotics and carcinostatic substance to blood vessel, urinary bladder and the like, there has been used an infusor of liquid drug with a bladder wherein liquid drug is charged into the bladder made of elastic material and liquid drug is dispensed into blood vessel and the like for a relatively long period of time with the use of shrinkage force of the bladder. The present applicant proposed a liquid infusion device which was improved from a viewpoint of prevention of leakage of liquid drug and prevention of contamination of bacteria and the like into liquid drug (Japanese Unexamined Patent Publication No. 135360/1989).
The liquid infusion device described in the above publication comprises, as shown in FIGS. 10 and 11, a bladder assembly a, a housing b for containing the bladder assembly a, a flow-regulating portion c having an injection needle 130 and a pipe 131 with small holes. The bladder assembly a comprises, as shown in FIG. 11, a tubular outer shaft 132, an inner shaft 133 slidably received within the outer shaft 132, a bladder 134 made of elastic material and placed outside the outer shaft and inner shaft wherein one end of the bladder is tightly fixed to the outer shaft 132 and the other end of the bladder is tightly fixed to the inner shaft 133, and a plug for injecting liquid drug into the bladder provided in the end portion of the outer shaft 132 opposite to the end whereinto the inner shaft 133 is inserted.
In using the above-mentioned liquid infusion device, the plug 135 is pricked with an injection needle of an injector, and liquid drug is charged into the bladder 134. After a predetermined amount of liquid drug is charged into the bladder 134, the injector is pulled out from the plug 135. Then, the plug 135 is pricked with the injection needle 130 of the flow-regulating portion c. The dispensation of liquid drug into the body of a human patient is carried out after prescribed operation such as air venting.
According to the liquid infusion device described in the above-mentioned publication, a closed-type housing is used so that superior effects such as prevention of leakage of liquid drug even if the bladder is broken can be obtained. However, a certain degree of clearance is required between the inner surface of an outer shaft and the outer surface of an inner shaft, because liquid drug is designed to flow out from an end of the outer shaft and therefore the inside of the outer shaft functions as not only moving space of the inner shaft but also passage of liquid drug. Accordingly, there is a problem that a certain degree of liquid drug remains within the outer shaft after the bladder perfectly shrinks. When using expensive liquid drug such as morphine hydrochloride and carcinostatic substance, a large amount of remaining liquid drug becomes a serious problem economically. Therefore, it has been desired to reduce the amount of remaining liquid drug as much as possible in the bladder.
The present invention was made to solve the drawbacks of the conventional liquid infusion device mentioned above, and it is an object of the present invention to provide a liquid infusion device capable of greatly reducing the amount of liquid drug remaining in the bladder.